1. Field of the Invention
The present invention relates to information storage techniques. More particularly, the present invention relates to a system for storing information in an information storage medium, such as a magnetic disk drive, a magnetic tape, a magnetic strip, such as on a credit card or a smart card, or an optical disk drive.
2. Description of the Related Art
FIG. 1 shows a high RPM disk drive 10 having a two-stage, or piggy-back, servo system for positioning a magnetic read/write head (or a recording slider) over a selected track on a magnetic disk 11. The two-stage servo system includes a voice-coil motor (VCM) 13 for coarse positioning a read/write head suspension 12 and a microactuator, or micropositioner, for fine positioning the read/write head over the selected track in a well-known manner. FIG. 2 shows an enlarged exploded view of the read/write head end of suspension 12. An electrostatic rotary microactuator 14 is attached to a gimbal structure 15 on suspension 12, and a slider 16 is attached to the microactuator. A read/write head 17 is fabricated as part of slider 16.
Data is stored on magnetic disk 11 by forming magnetic transitions on the surface of magnetic disk 11 using read/write head 17 in a well-known manner. As the storage capacity of a magnetic disk, such as disk 11, increases, the surface area covered by an individual bit must correspondingly decrease. Reducing the size of the area covered by an individual bit has limits. That is, the grains of magnetic material forming the disk are currently approaching a size where the normal thermal fluctuations of magnetization at room temperature is enough to spontaneously change the magnetization of a grain from one magnetic direction to another. This phenomenon is known as the superparamagnetic effect.
Concern over the superparamagnetic effect will likely force a change of technology in order to insure that areal densities of magnetic media can continue to be increased without sacrificing customer data. An approach to overcome the limits caused by the superparamagnetic effect is perpendicular recording, in which the magnetic fields of the grains point substantially out of or into the disk rather than opposite directions across the disk surface. A consequence of perpendicular recording is that it is possible to achieve higher write fields using perpendicular heads, thus enabling recording of media having higher magnetic anisotrophy and greater thermal stability.
Another proposed solution for providing high-density recording is to use patterned media containing a uniform array of bits, with each bit being formed from a single grain of magnetic material instead of hundreds of grains. See, for example, M. Todorovic et al., Writing and reading of single magnetic domain per bit perpendicular patterning media, Applied Physics Letters, Volume 74, Number 17, 26 Apr. 1999, pp. 2516-2518; U.S. Pat. No. 5,587,223 to White; and U.S. Pat. No. 5,820,769 to Chou.
While the bit width of a patterned media can be made very small, the bit length may not be reduced as much as compared to conventional non-patterned media techniques. Consequently, the data rate that is achievable using a patterned media will be adversely impacted in the absence of resorting to much higher media RPM. Moreover, it will be more difficult to fabricate read and write heads to address the narrower tracks provided by patterned media.
What is needed is a technique for optimizing the overall performance of a storage system, particularly with respect to key attributes, such as areal density and data rate, and that takes into account limitations to the current state of the art of minimum resolutions that are achievable using both patterned media and read and write head design.